1. Field of the Invention
The present invention relates in general to fluid flow and combustion diagnostics and, more particularly, to fiber-optic probes to aid in the measurements of various parameters in reacting and non-reacting flows.
2. Description of the Related Art
Engineering design of many devices of practical significance rely heavily on the availability of experimental data for either validation of computer-aided design or information on controlling phenomena to aid in the design process. For example, in many and most applications involving reacting and non-reacting flows, information about three-dimensional flow velocity, concentration fields of various species, and temperature are important variables to know in order to properly predict flow behavior in, for example, automobile engines, gas turbines, industrial furnaces, and many other applications.
In the past intrusive probes were used to make measurements, but the introduction of probes in the flow fields raises questions on the accuracy of the data collected. In order to minimize flow disturbance due to measurements, many laser-based experimental techniques have been developed, as for example, Laser Doppler Velocimeter or Anemometry, LDV or LDA; Phase Doppler Particle Analyzer, or PDPA; Particle Image Velocimetry, or PIV, Laser Induced Florescence, or LIF; Laser Induced Incandescense, or LII; and Coherent Anti-Stokes Raman Spectroscopy, or CARS. However, in view of the many supporting devices needed to make these laser-based techniques to work combined with the difficulty in accessing the flow field to be studied, in many applications, an optical probe is needed to collect measurement information to be further processed into useful data. Although the following discussion will use an automobile engine as an example, those of ordinary skill in the art will appreciate that the instant invention is equally applicable to other engineering application areas, such as, but not limited to, gas turbine engines, air and water flows, industrial furnaces, and boilers, to name a few.
Engine performance is influenced by many factors, such as the combustion chamber design, intake exhaust ports design and location, combustion process, turbulence intensity in-cylinder, fuel-air mixing process, etc., and much research has been devoted to investigate these effects on the Internal Combustion, or IC, engine behavior. However, the flow field inside the cylinder of an IC engines is still not well understood due to the complexity of the flow and also due to the lack of experimental instrumentation. The flow characteristics inside the cylinder of IC engine can be summarized as follows: (1) unsteady or non-stationary as a result of the reciprocating piston motion; (2) turbulent at all engine speeds and inlet port/cylinder dimensions; (3) three dimensional as a result of the engine geometry; (4) as having local variations from cycle-to-cycle; (5) as having time scales associated with the bulk flow variations of the same order as the turbulent time scales; and (6) spatially confined by time-varying flow boundaries of rather complex geometry.
In-cylinder flow characteristics of IC engines play a crucial role in engine performance since it affects the combustion process, and thus the efficiency of the engines directly. Understanding the flow physics of in-cylinder motions, such as tumble and swirl, requires the measurement of velocity distribution, turbulent intensity within the engine cylinder and other parameters. In this vain many researchers have employed different experimental and computational techniques, including hot-wire anemometry, Particle Tracking Velocimetry, or PTV, PIV, and LDA techniques. Among these techniques, as noted by Arcoumanis and Whitelaw (C. Arcoumanis and J. H. Whitelaw “Fluid Mechanics of Internal Combustion Engines: A Review”, International Symposium on Flows in Internal Combustion Engines-III., Vol. 28, ASME 1985, the entire contents of which are hereby incorporated by reference) LDA has been widely used since the LDA can be easily adapted to study flow fields within hard to reach geometries such as the valve exit flow, and the flow inside complex bowl-piston configurations. LDA has also been successfully employed to identify the flow affects on combustion within the engine cylinders (Id.). LDA, similar to the other optical technique, allows non-intrusive measurements of the flow field.
Computation of in-cylinder flows prove to be difficult due to the lack of turbulence models, further experimental data is required to improve predicting capability of computational codes. There is a need for further experimental data at several points in different planes inside the cylinder to further understand the flow behavior inside the cylinder effectively. Investigation of such a flow requires special instruments and several such instruments have been developed by the researchers over the years, as briefly summarized herein below.
NeuBer et al. (H-J. NeuBer, L. Spiegel and J Ganser, “Particle Tracking Velocimetry-A Powerful Tool to Shape the In-Cylinder Flow of Modern Multi Valve Engine Concepts,” SAE Paper, 950102, 1995, the entire contents of which are herein incorporated by reference) have used a PTV technique to analyze in cylinder flow. Their study was aimed to parametrically study the effect of the intake port configurations. They tested port configurations resulting in high and low tumble levels or in different levels of swirl. The authors have investigated the tumble levels, turbulent intensity and the transient flow structure related processes in the combustion chamber, and they observed that, since the intake ports induce the formation and development of the tumble, the design of the intake ports is important for controlling the in-cylinder flow. Patrie and Martin (Mitchell P. Patrie and Jay K. Martin, “PIV Measurements of In-Cylinder Flow Structures and Correlation With Engine Performance”, ICE-Vol. 29-3, 1997 Fall Technical Conference, ASME 1997, the entire contents of which are herein incorporated by reference) have also investigated the effects of the design of intake ports on producing swirl and/or tumble motions in the cylinder of engines by using PIV technique, and they also observed that in-cylinder flow field turbulence can enhance combustion, yielding shorter burn times, reducing emissions, and improving fuel economy.
Lee et al. (Ki Hyung Lee and Chang Sik Lee Hyun Jong Park and Dae Sik Kim, “Effects of Tumble and Swirl Flows on The Turbulence Scale Near the TDC in 4 Valve S.I. Engine”, ICE-Vol. 36-2, 2001 ICE Spring Technical Conference—Vol. 2, ASME 2001, the entire contents of which are herein incorporated by reference) have investigated the effects of the design of the combustion chamber and the intake manifold on the flow characteristics inside the cylinder of a laboratory IC engine. They developed single frame PTV and two color PIV systems to investigate the influences of the swirl and the tumble intensifying system on the in-cylinder flow characteristics under the various intake geometries.
Vigor et al. (H. Vigor, J. Pecheux, and J. L. Peube, “Velocity Measurements Inside The Cylinder of An Internal Combustion Model Engine During The Intake Process”, Laser Anemometry, Vol. 1, ASME 1991, the entire contents of which are herein incorporated by reference) have focused on the flow field near the walls of the internal combustion chambers. They used LDA to measure the boundary layer flow on the cylinder walls during the intake process on a laboratory engine. Measurements were made while the intake velocity was constant, which resulted in a flow field without the swirl within the engine. Their measurement of the axial velocity and the turbulent kinetic energy profiles at different regions of the cylinder revealed that the boundary layer was two dimensional in nature. Flow visualization results also confirmed this observation.
Himes and Farell (Michael R. Himes' Patrick V. Farell, “Laser Doppler Velocimeter Measurements within a motored Direct Injection Spark Ignited Engine”, ICE-Vol. 31-2, 1998 Fall Technical Conference ASME 1998, the entire contents of which are herein incorporated by reference) studied the affect of the in-cylinder flow on the mixing process in an engine operated as a direct injection spark ignited engine. They used LDV technique to quantify the velocities and the turbulence levels in the regions where the fuel would be injected additional to the measurements at several different locations.
Beside experimental works, computational works have also been performed to understand the flow behavior inside the cylinder of engines. The most famous code developed for this purpose is known as KIVA-3. Kong and Hong (Song-Charng Kong Che-Wun Hong, “Comparison of Computed and Measured Flow Processes in A Four Stroke Engine”, ICE—Vol. 29-2, 1997 Fall Technical Conference, ASME 1997, the entire contents of which are herein incorporated by reference) used the KIVA-3 code with improved submodels they developed to investigate the flow structures, velocities, and turbulent parameters, by assuming that turbulent intensity is 10% of the mean inlet velocity, and the inlet turbulent integral scale is 10% of the intake pipe diameter. Authors compared their computational results with the experimental data obtained using LDA technique, and they showed that the comparisons of computed and measured flow velocities at three different cross sections agreed reasonably well. The agreement of the computed and measured integral length scales were satisfactory once the complexity of the engine turbulence is taken into account. In another computational work, the Conchas-Spray model was used by Kuo and Duggal (T. W. Kuo and V. K. Duggal, “Modeling of In-Cylinder Flow Characteristics-Effect of Engine Design Parameters”, Flows in Internal Combustion Engines-II, ASME 1984, the entire contents of which are herein incorporated by reference) to investigate the flow characteristics and the effects of the different piston bowl shapes on the flow behavior.
Many parameters, such as the combustion chamber geometry, intake port valve/manifold geometry and location, affect the flow turbulence, swirl, tumble and the flow velocities. The flow parameters in turn affect the fuel-air mixing, and the combustion processes (flame speed), which are directly related to the efficiency and the emissions of the engine. As noted by Rask (Rodney B. Rask, “Laser Doppler Anemometer Measurements in an Internal Combustion Engine”, SAE Paper, 790094, 1979, the entire contents of which are herein incorporated by reference) measurements of the flow variables in engines with different configurations are required to improve their efficiencies.
For better understanding the flow inside the cylinder, researchers have developed novel probes that can be used in off-the-shelf operating engines. Ikeda et al. (Ikeda, Y., Nishihara., H., Nakajima, T., 2000, “Spark plug-in Fiber LDV for Turbulent Intensity Measurement of Practical SI Engine”, 10th International Symposia on Applications of Laser Techniques to Fluid Mechanics, July 10-13, Lisbon, Portugal, the entire contents of which are herein incorporated by reference) and Kim et al. (Kim, B., Kaneko, M. and Mitani, M., Y. Ikeda and Nakajima, “In-Cylinder Turbulent Measurements with a Spark Plug-In Fiber LDV”, 11th Symposia on Applications of Laser Techniques to Fluid Mechanics, July 8-11, Lisbon Portugal, the entire contents of which are herein incorporated by reference) have developed a non-traversable LDV probe which could fit into M14 size spark plug to measure turbulence at the spark plug location under motored engine conditions. Bopp et al. (Bopp, S., Durst, F., Tropea, C., “In-Cylinder Velocity Measurements with a Mobile Fiber Optic LDA System”, SAE Paper, 900055, 1990, the entire contents of which are herein incorporated by reference) have designed fiber optic, one component LDV probe to investigate the flow characteristics inside the research engine.
Due to the high pressures and temperatures obtained during the combustion process, measurements with these techniques are usually accomplished in motored engines, in cold flow conditions and at engine speeds lower than the operation speeds of the commercial engines. Reviews of the recent state-of-the-art techniques used in flow field investigation of fired production engines are reported in the literature. See, for example, Hassel and Linow (Hassel, E. P. and Linow S., 2000, “Laser diagnostics for studies of turbulent combustion”, Meas. Sci. Technol. 11 (2000) R37-R57, the entire contents of which are herein incorporated by reference) Zhao and Ladommatos (H. Zhao and N. Ladommatos, 1998, “Optical Diagnostics for In-cylinder Mixture Formation Measurements in IC Engines”, Prog. Energy Combust. Sci. Vol. 24, pp. 297-336, the entire contents of which are herein incorporated by reference), Kuwahara (K. Kuwahara, 2003, “In-Cylinder Phenomena Diagnostics for Gasoline Engine Development”, Technical Review, vol 15., pp. 21-31, the entire contents of which are herein incorporated by reference), and Kuwahara and Ando (Kuwahara and H. Ando, 2000, “Diagnostics of in-cylinder flow, mixing and combustion in gasoline engines”, Meas. Sci. Technol. Vol. 11, pp. R95-R111, the entire contents of which are herein incorporated by reference). These papers point to the fact that very expensive engines with very specialized optical access ports are required for laser-based diagnostics, and the measurements can only be made in reduced RPM conditions. In addition, conventional probes are not traversable, are not capable of measuring two- or three-components of velocity, comprise many moving parts, are not suitable for making measurements in production car engines, and are not designed using off-the shelf optical components.
Therefore, based at least on the foregoing summarized discussion, a need exist for a miniature, fiber-optic, traversable probe. This novel, fiber-optic probe includes several unique capabilities, including, as non-limiting examples: (1) miniature, fiber optic, two component LDV capability; (2) traversable along the spark-plug axis for measurements at several point; (3) suitable for measurements in production car engines; (4) capable of measuring shear stresses and normal stresses both in cold and hot flows; and (5) designed using off-the shelf optics, without any moving parts which makes the probe suitable for very cramped, and highly vibrational environments. In one embodiment, the probe fits into a spark plug opening in an operating off-the shelf car engine, and is capable of measuring two velocity components simultaneously in the directions perpendicular to the spark plug axis at several points including the spark plug location within the cylinder.